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Kazuhiro Kogame - One of the best experts on this subject based on the ideXlab platform.
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Geographic parthenogenesis in the brown alga Scytosiphon Lomentaria (Scytosiphonaceae): sexuals in warm waters and parthenogens in cold waters
2021Co-Authors: Masakazu Hoshino, Mitsunobu Kamiya, Shimpei Hiruta, Maria Croce, Takahiro Jomori, Toshiyuki Wakimoto, Kazuhiro KogameAbstract:Geographic parthenogenesis (GP), a phenomenon where parthenogens and their close sexual relatives inhabit distinct geographic areas, has been considered an interesting topic to understand the adaptation to marginal habitats and the role of hybridization in evolution. Reports of GP from land and freshwater are numerous, however, this occurrence has been rarely reported on from the sea. Brown algae are mostly marine and are thought to include numerous obligate parthenogens; still, little is known about the distribution, origin, and evolution of parthenogens in this group. Here we report a novel pattern of GP in the isogamous brown alga Scytosiphon Lomentaria. Sex ratio investigation demonstrated that, in Japan, sexual populations grew in the coast along warm ocean currents, whereas female-dominant parthenogenetic populations grew mainly in the coast along a cold ocean current. In the two localities where sexual and parthenogenetic populations were parapatric, parthenogens grew in more wave-exposed areas than sexuals. Population genetic and phylogenetic analyses, including those based on genome-wide single nucleotide polymorphism data, suggested that: (1) parthenogens evolved at least twice in S. Lomentaria, (2) parthenogens did not originate from inter-species hybridization, (3) new parthenogenetic lineages have arisen from hybridizations between parthenogens and sexuals, and (4) parthenogens have a wider distribution than sexuals. We also showed that the production of sex pheromones, which attract male gametes, has been independently suppressed/lost in two parthenogenetic lineages. This parallel suppression/loss of the sexual trait may represent the direct origin of parthenogens, or the regressive evolution of a useless trait under asexuality.
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Systematics, distribution, and sexual compatibility of six Scytosiphon species (Scytosiphonaceae, Phaeophyceae) from Japan and the description of four new species.
Journal of phycology, 2020Co-Authors: Masakazu Hoshino, Masanori Hiraoka, Atsuko Tanaka, Mitsunobu Kamiya, Shinya Uwai, Kazuhiro KogameAbstract:The brown alga Scytosiphon Lomentaria (Scytosiphonaceae, Ectocarpales) has been reported from cold and warm waters worldwide. Although previous molecular phylogenetic studies and crossing experiments have shown that it is a complex of multiple distinct species, the taxonomic position and accurate distribution of each species have remained largely unclear. For the S. Lomentaria complex from Japan, our cox1 and rbcL phylogenetic analyses detected six species. In addition to five previously detected species (species Ia-Va), one species (species VI) was newly found in the subtropical area, Okinawa Island. Species VI was recovered as a sister to species Ia-Va in rbcL. Based on the morphological and phylogenetic data, we concluded that species Ia is S. Lomentaria, species IIIa is S. promiscuus, and the other four species are newly described: S. shibazakiorum for species IIa, S. tosaensis for species IVa, S. arcanus for species Va, and S. subtropicus for species VI. The cox1-based analysis also showed that S. Lomentaria, S. shibazakiorum, and S. promiscuus have worldwide distributions, while the other three species were not found outside of Japan. In Japan, except for S. subtropicus, distributions of these species overlapped. Our crossing experiments showed that gametic incompatibility (pre-zygotic barrier) was less developed between the allopatric species (i.e., S. subtropicus and others) compared with the sympatric species. It may suggest that pre-zygotic barriers have evolved among the sympatric species due to reinforcement.
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Parthenogenetic female populations in the brown alga Scytosiphon Lomentaria (Scytosiphonaceae, Ectocarpales): decay of a sexual trait and acquisition of asexual traits.
Journal of phycology, 2018Co-Authors: Masakazu Hoshino, Tatsufumi Okino, Kazuhiro KogameAbstract:In isogamous brown algae, the sexuality of populations needs to be tested by laboratory crossing experiments, as the sexes of gametophytes are morphologically indistinguishable. In some cases, gamete fusion is not observed and the precise reproductive mode of the populations is unknown. In the isogamous brown alga Scytosiphon Lomentaria in Japan, both asexual (gamete fusion is unobservable) and sexual populations (gamete fusion is observable) have been reported. In order to elucidate the reproductive mode of asexual populations in this species, we used PCR-based sex markers to investigate the sex ratio of three asexual and two sexual field populations. The markers indicated that the asexual populations consisted only of female individuals, whereas sexual populations are composed of both males and females. In culture, female gametes of most strains from asexual populations were able to fuse with male gametes; however, they had little to no detectable sexual pheromones, significantly larger cell sizes, and more rapid parthenogenetic development compared to female/male gametes from sexual populations. Investigations of sporophytic stages in the field indicated that alternation of gametophytic and parthenosporophytic stages occur in an asexual population. These results indicate that the S. Lomentaria asexual populations are female populations that lack sexual reproduction and reproduce parthenogenetically. It is likely that females in the asexual populations have reduced a sexual trait (pheromone production) and have acquired asexual traits (larger gamete sizes and rapid parthenogenetic development).
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Concordance between DNA-based species boundaries and reproductive isolating barriers in the Scytosiphon Lomentaria species complex (Ectocarpales, Phaeophyceae)
Phycologia, 2018Co-Authors: Masakazu Hoshino, Shozo Ishikawa, Kazuhiro KogameAbstract:Abstract: DNA-based species delimitation methods often predict many putative cryptic species. Interpretation of these putative species (i.e. do they represent distinct species, or is this an erroneous estimate based on DNA variability?) is challenging because estimates of DNA-based delimitation are often difficult to verify using nongenetic data such as morphology or geographical distribution. In the present study, estimates of DNA-based delimitation methods were verified based on the biological species concept in Japanese populations of Scytosiphon Lomentaria. Three DNA-based species delimitation methods (Generalised Mixed Yule Coalescent, Poisson Tree Processes and Automatic Barcode Gap Discovery) were conducted using mitochondrial (cox1) and nuclear (second intron of centrin gene) DNA sequence datasets. In the S. Lomentaria species complex, five putative cryptic species (Ia–Va) were well-supported by DNA-based species delimitation, and these putative species were often found in the same locality. To ve...
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Genetic diversity and mitochondrial introgression in Scytosiphon Lomentaria (Ectocarpales, Phaeophyceae) in the north-eastern Atlantic Ocean
Phycologia, 2015Co-Authors: Kazuhiro Kogame, Fabio Rindi, Akira F. Peters, Michael D. GuiryAbstract:Abstract: The common brown alga Scytosiphon Lomentaria (Scytosiphonaceae) has generally been regarded as a species complex. In the Pacific, molecular data have shown that it includes more than one species; the diversity in other oceans, however, has not been examined. In the present study, the genetic diversity of S. Lomentaria was investigated in 57 samples from the north-east Atlantic (mainly from Ireland) and two from the Mediterranean, which were compared with seven samples from Japan. Phylogenetic analyses based on the mitochondrial cytochrome oxidase subunit 3 gene (cox3) and nuclear ribosomal internal transcribed spacers (ITS1 and 2) revealed four separate monophyletic groups. Clades A1 and A2 consisted of the samples from the north-east Atlantic; the Mediterranean samples also belonged to A1. The affiliation of four samples was incongruent between cox3 and ITS trees, suggesting directional mitochondrial introgression from A2 to A1. Clades P1 and P2 contained nine samples from the north-east Atlant...
Juan A. Correa - One of the best experts on this subject based on the ideXlab platform.
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Seaweeds early development: detrimental effects of desiccation and attenuation by algal extracts
Planta, 2011Co-Authors: Loretto Contreras-porcia, Daniela Thomas, Sebastián Callejas, Aníbal Contreras, Ana Lafuente, María Rosa Flores-molina, Camille Sordet, Georg Pohnert, Juan A. CorreaAbstract:The effects of desiccation on the early development stages of Mazzaella laminarioides, Scytosiphon Lomentaria and Lessonia nigrescens, algal species with different patterns of distribution across the intertidal zone, were examined in the laboratory. In addition, the protective effect against desiccation was evaluated using algal extracts, including those from Porphyra columbina, a macroalga tolerant to desiccation that lives in the uppermost part of the intertidal zone. Our results showed that M. laminarioides displayed the highest resistance to daily desiccation, followed by S. Lomentaria, whereas L. nigrescens was the most susceptible. Spores from L. nigrescens exposed to desiccation, although being able to germinate, ceased further post-germination development. In addition, our results showed that all species exposed to extracts from desiccated P. columbina successfully completed their development and strongly suggest the occurrence of compounds with protective properties that help in attenuating the stress caused by desiccation. Finally, our results indicate that the magnitude of the effects generated by desiccation on the early algal development is related to the position of the species in the intertidal zone, and that the protective effects of P. columbina extracts reveal an exceptional metabolism of this species under desiccation stress.
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differential responses to copper induced oxidative stress in the marine macroalgae lessonia nigrescens and scytosiphon Lomentaria phaeophyceae
Aquatic Toxicology, 2009Co-Authors: Loretto Contreras, Daniella Mella, Alejandra Moenne, Juan A. CorreaAbstract:Abstract In order to help explain the absence of the brown kelp Lessonia nigrescens from a coastal environment chronically enriched with copper, we characterized the biochemical responses induced by copper stress in this kelp and compared them with those displayed by the copper tolerant brown alga Scytosiphon Lomentaria . These algae were cultivated with increasing concentrations of copper (20, 40 and 100 μg L −1 ) for 96 h and the temporal production of hydrogen peroxide, superoxide anions and lipoperoxides as well as the activities of antioxidant enzymes catalase (CAT), glutathione peroxidase (GP), ascorbate peroxidase (AP), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) and the activity of the defense enzyme lipoxygenase (LOX) were determined. In L. nigrescens and S. Lomentaria , a single peak of hydrogen peroxide was detected, with similar maxima after 3 h of copper exposure, although in L. nigrescens buffering took longer. Superoxide anions, on the other hand, were only detected in L. nigrescens . The production of lipoperoxides in L. nigrescens increased steadily at higher copper levels, in a pattern clearly different to their rapid stabilization in S. Lomentaria . We suggest that the accumulation of lipoperoxides might be related to LOX, whose activity also increases with exposure time. Furthermore, activities of the antioxidant enzymes CAT, GP, AP and DHAR were lower in L. nigrescens than in S. Lomentaria , and GP and DHAR were completely inhibited at higher copper concentrations. Since these enzymes also detoxify fatty acid hydroperoxides, their inhibition, together with the activation of LOX, may explain the persistent and copper-dependent levels of lipoperoxides in L. nigrescens . Based on terrestrial plant models demonstrating toxic effects of lipoperoxides, and on our results on organellar ultrastructural changes, we suggest that copper toxicity induced an uncontrolled lipoperoxide accumulation which may lead to cell damage and dysfunction in L. nigrescens , explaining at least partially, the absence of this kelp in a copper-enriched coastal environment.
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Molecular and morphologically distinct Scytosiphon species (Scytosiphonales, Phaeophyceae) display similar antioxidant capacities
Journal of Phycology, 2007Co-Authors: Loretto Contreras, Alejandra Moenne, Geraldine Dennett, R. Eduardo Palma, Juan A. CorreaAbstract:The taxonomic status of an alga with complanate thalli, occurring in central Chile and belonging to the genus Scytosiphon, was elucidated. Morphological and molecular features demonstrated that, in addition to the known and widespread constricted S. Lomentaria (Lyngb.) Link that occurs along the Chilean coast, there is a Scytosiphon with complanate thalli that occurs only in central Chile—S. gracilis Kogame. Morphological analyses of this previously unreported complanate Scytosiphon showed thalli without constrictions, coherent plurilocular sporangia without ascocysts, and phaeophycean hairs arising from cortical cells. Furthermore, sequences of the internal transcribed spacer (ITS1 and ITS2) regions of the complanate Scytosiphon were 99.8% and 100% identical to those detected in S. gracilis from Korea. ITS-based comparative analyses showed that complanate Scytosiphon grouped in a different clade than S. Lomentaria and S. tenellus Kogame from various parts of the world, including Chilean species. Moreover, molecular analyses suggest the occurrence of two distinct ITS types of S. Lomentaria in northern Chile, corresponding to the Korean and Greek types. On the other hand, biochemical analyses of copper-induced antioxidant responses in S. gracilis and S. Lomentaria showed an identical increase in antioxidant enzyme activities. These results suggest that copper tolerance might be a constitutive trait in these species of Scytosiphon.
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antioxidant responses in scytosiphon Lomentaria phaeophyceae inhabiting copper enriched coastal environments
Journal of Phycology, 2005Co-Authors: Loretto Contreras, Alejandra Moenne, Juan A. CorreaAbstract:Scytosiphon Lomentaria (Lingb.) Link. (Phaeophyceae) is one of the two dominant seaweeds in a coastal area of northern Chile affected by copper mine wastes, where the concentration of copper in water and algal tissues remains higher than in non-impacted sites. Copper-loaded plants develop oxidative stress, as demonstrated by the increased levels of reactive oxygen species and lipoperoxides. This stress was associated with 1) an enhanced activity of the antioxidant enzymes catalase, glutathione peroxidase, ascorbate peroxidase, monodehydroascorbate reductase, and dehydroascorbate reductase and 2) an inhibition of the glutathione reductase activity. Furthermore, stressed plants showed a decrease in glutathione and phenolic compounds levels and an increase in total ascorbate. Reciprocal transplants revealed that plants rapidly adjusted their antioxidant system in response to the conditions of the receiving site. In individuals transplanted from the copper-enriched environment to the control site, normal levels of lipoperoxides and antioxidant compounds were restored in 48 h and antioxidant enzymes recovered their basal activities in 96 h. Individuals transplanted from the control site to the copper-enriched area adjusted their antioxidant compounds and antioxidant enzymes within 48 h and 96 h, respectively, and reached the functional status of the local plants. We conclude that S. Lomentaria inhabiting the copper-enriched area buffered oxidative stress by a simultaneous involvement of antioxidant enzymes and water-soluble antioxidant compounds. These antioxidant responses were rapid and reversible, suggesting that copper resistance in S. Lomentaria is a constitutive trait and that copper enrichment of the area did not result in a locally adapted copper-tolerant ecotype.
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DIFFERENTIAL LIFE HISTORY PHASE EXPRESSION IN TWO COEXISTING SPECIES OF SCYTOSIPHON (PHAEOPHYCEAE) IN NORTHERN CHILE1
Journal of Phycology, 2005Co-Authors: Carolina Camus, Andrés P. Meynard, Sylvain Faugeron, Kazuhiro Kogame, Juan A. CorreaAbstract:The identity of two phaeophycean taxa that monopolized the middle-lower rocky intertidal zone of a coastal area chronically exposed to copper mine wastes in northern Chile was unraveled. One of them was preliminarily identified as the gametophytic stage of Scytosiphon Lomentaria (Lyngbye) Link. The other, a dark crust, resembled the alternate stage of some Scytosiphon species. Comparative analysis of morphology, life history, and DNA sequences strongly suggests that crusts corresponded to sporophytic S. tenellus Kogame and confirm that erect thalli belonged to S. Lomentaria. A clear segregation of erect and crustose thalli was found using internal transcribed spacer region 1 and RUBISCO spacer sequences. Furthermore, whereas crusts always grouped with S. tenellus, erect thalli always grouped with S. Lomentaria. Life history studies failed to connect the two entities. First, field-collected S. tenellus produced progeny that either recycled the crust, which reproduced by unilocular zoidangia, or developed into erect thalli. The latter, unlike typical gametophytic S. Lomentaria, developed patchy sori of plurilocular zoidangia. Second, S. Lomentaria displayed a direct-type life cycle, in which progeny from erect individuals only developed into erect thalli and produced only plurilocular zoidangia. This constitutes the first experimental study on Scytosiphon from the Pacific coast of South America and the first report of S. tenellus on this coast. It is also the first report of the crustose stage of Scytosiphon appearing as a perennial and dominant algal species in a temperate rocky intertidal system.
Taizo Motomura - One of the best experts on this subject based on the ideXlab platform.
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Identification and characterization of a fluorescent flagellar protein from the brown alga Scytosiphon Lomentaria (Scytosiphonales, Phaeophyceae): A flavoprotein homologous to Old Yellow Enzyme
European Journal of Phycology, 2005Co-Authors: Satoshi Fujita, Taizo Motomura, Mineo Iseki, Yumiko Makino, Hiroshi Kawai, Shinya Yoshikawa, Masakatsu Watanabe, Akio MurakamiAbstract:The posterior flagellum of the zoospore of the brown alga Scytosiphon Lomentaria exhibits bright green autofluorescence. To identify the fluorescent flagellar substance(s), we isolated flagella from zoospores and partially purified a flavoprotein by anion-exchange and gel-filtration chromatography. Spectrofluorometric and chromatographic analyses showed that the flavoprotein had an apparent molecular mass of 41 kDa and a non-covalently bound flavin mononucleotide as a chromophore. Based on partial amino acid sequences of the protein, a cDNA of the 41-kDa flavoprotein was cloned and sequenced. The deduced amino acid sequence of the cDNA was homologous to that of the Old Yellow Enzyme family distributed in proteobacteria, yeasts and vascular plants.
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NEW PYRENOID FORMATION IN THE BROWN ALGA, SCYTOSIPHON Lomentaria (SCYTOSIPHONALES, PHAEOPHYCEAE)1
Journal of Phycology, 2002Co-Authors: Chikako Nagasato, Taizo MotomuraAbstract:The Scytosiphon Lomentaria (Lyngbye) Link cell characteristically has only one chloroplast with a prominent protruding pyrenoid. We observed the appearance of a new pyrenoid in each chloroplast during first mitosis in zygotes of S. Lomentaria, using the freeze substitution technique. At first, a pyrenoid matrix appeared within the outermost stroma, in which thylakoid triplets and ribosomes were absent. At this time, the surface of this part remained smooth. The old pyrenoid was covered with a pyrenoid cap on the cytoplasmic side, whereas there was no pyrenoid cap on the new pyrenoid before protrusion. Irregularly shaped membranous sacs containing fine granular materials associated with the cytoplasmic side of the new pyrenoid. The sacs fused with each other and changed conformation and finally transformed into the pyrenoid cap. The new pyrenoid gradually protruded toward the cytoplasm, and the new pyrenoid cap became curved along the surface of pyrenoid. Cytokinesis occurred, and each chloroplast had two prominent protruding pyrenoids in two-celled zygotes. We examined immunolocalization of β-1,3-glucans within the pyrenoid cap with a monoclonal antibody, using EM. Gold particles indicating localization of β-1,3-glucans were detected in vacuoles but never in the pyrenoid cap. This observation suggests that the pyrenoid cap in brown algae contains no photosynthetic products such as polysaccharide.
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Spindle formation in karyogamy-blocked zygotes of the isogamous brown alga Scytosiphon Lomentaria (Scytosiphonales, Phaeophyceae)
European Journal of Phycology, 2000Co-Authors: Chikako Nagasato, Taizo Motomura, Terunobu IchimuraAbstract:The first spindle formation in karyogamy-blocked zygotes in the isogamous brown alga Scytosiphon Lomentaria was studied by electron and immunofluorescence microscopy using anti-centrin and anti-β-tubulin antibodies. Zygotes blocked in karyogamy by incubation at high temperature (22 °C) were compared with normal zygotes incubated at 14 °C. In normal zygotes, after the disappearance of female gamete centrioles, centrioles from the male gamete duplicated and migrated to both poles in the metaphase, and a bipolar spindle was formed. The nuclear envelope was almost intact except at the poles. In karyogamy-blocked zygotes of S. Lomentaria, both DNA synthesis and chromosomal condensation occurred in the male and female nuclei. A bipolar mitotic spindle with a pair of centrioles at each of two poles could be observed in the male nucleus, but not in the female nucleus. In some cases, after a pair of centrioles derived from the male gamete duplicated and separated, one of the two pairs migrated towards the female n...
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KARYOGAMY BLOCK BY HEAT STRESS IN THE FERTILIZATION OF BROWN ALGAE
Journal of Phycology, 1999Co-Authors: Chikako Nagasato, Taizo Motomura, Terunobu IchimuraAbstract:Karyogamy was inhibited by heat stress in zygotes of Scytosiphon Lomentaria (Lyngbye) Link (isogamy), Cutleria cylindrica Okamura (anisogamy), and Fucus distichus subsp. evanescens (C. Agardh) Powell (oogamy). Although high temperatures did not inhibit migration of the male and female nuclei, nuclear envelope fusion was blocked. The ultrastructural stage at which karyogamy was inhibited varied among these species. In S. Lomentaria, the outer membranes fused with each other, but the inner membranes did not fuse. Partial fusion of the nuclear envelope occurred in C. cylindrica. In F. distichus, the block of karyogamy at high temperature was incomplete, and nuclear fusion proceeded gradually. The block to karyogamy in S. Lomentaria zygotes was reversible, and karyogamy proceeded when zygotes were transferred from 22° to 14° C. Experiments using inhibitors suggested that proteins that might be formed de novo after fertilization do not participate in karyogamy or its inhibition at either 14° or 22° C.
Masakazu Hoshino - One of the best experts on this subject based on the ideXlab platform.
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Geographic parthenogenesis in the brown alga Scytosiphon Lomentaria (Scytosiphonaceae): sexuals in warm waters and parthenogens in cold waters
2021Co-Authors: Masakazu Hoshino, Mitsunobu Kamiya, Shimpei Hiruta, Maria Croce, Takahiro Jomori, Toshiyuki Wakimoto, Kazuhiro KogameAbstract:Geographic parthenogenesis (GP), a phenomenon where parthenogens and their close sexual relatives inhabit distinct geographic areas, has been considered an interesting topic to understand the adaptation to marginal habitats and the role of hybridization in evolution. Reports of GP from land and freshwater are numerous, however, this occurrence has been rarely reported on from the sea. Brown algae are mostly marine and are thought to include numerous obligate parthenogens; still, little is known about the distribution, origin, and evolution of parthenogens in this group. Here we report a novel pattern of GP in the isogamous brown alga Scytosiphon Lomentaria. Sex ratio investigation demonstrated that, in Japan, sexual populations grew in the coast along warm ocean currents, whereas female-dominant parthenogenetic populations grew mainly in the coast along a cold ocean current. In the two localities where sexual and parthenogenetic populations were parapatric, parthenogens grew in more wave-exposed areas than sexuals. Population genetic and phylogenetic analyses, including those based on genome-wide single nucleotide polymorphism data, suggested that: (1) parthenogens evolved at least twice in S. Lomentaria, (2) parthenogens did not originate from inter-species hybridization, (3) new parthenogenetic lineages have arisen from hybridizations between parthenogens and sexuals, and (4) parthenogens have a wider distribution than sexuals. We also showed that the production of sex pheromones, which attract male gametes, has been independently suppressed/lost in two parthenogenetic lineages. This parallel suppression/loss of the sexual trait may represent the direct origin of parthenogens, or the regressive evolution of a useless trait under asexuality.
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Systematics, distribution, and sexual compatibility of six Scytosiphon species (Scytosiphonaceae, Phaeophyceae) from Japan and the description of four new species.
Journal of phycology, 2020Co-Authors: Masakazu Hoshino, Masanori Hiraoka, Atsuko Tanaka, Mitsunobu Kamiya, Shinya Uwai, Kazuhiro KogameAbstract:The brown alga Scytosiphon Lomentaria (Scytosiphonaceae, Ectocarpales) has been reported from cold and warm waters worldwide. Although previous molecular phylogenetic studies and crossing experiments have shown that it is a complex of multiple distinct species, the taxonomic position and accurate distribution of each species have remained largely unclear. For the S. Lomentaria complex from Japan, our cox1 and rbcL phylogenetic analyses detected six species. In addition to five previously detected species (species Ia-Va), one species (species VI) was newly found in the subtropical area, Okinawa Island. Species VI was recovered as a sister to species Ia-Va in rbcL. Based on the morphological and phylogenetic data, we concluded that species Ia is S. Lomentaria, species IIIa is S. promiscuus, and the other four species are newly described: S. shibazakiorum for species IIa, S. tosaensis for species IVa, S. arcanus for species Va, and S. subtropicus for species VI. The cox1-based analysis also showed that S. Lomentaria, S. shibazakiorum, and S. promiscuus have worldwide distributions, while the other three species were not found outside of Japan. In Japan, except for S. subtropicus, distributions of these species overlapped. Our crossing experiments showed that gametic incompatibility (pre-zygotic barrier) was less developed between the allopatric species (i.e., S. subtropicus and others) compared with the sympatric species. It may suggest that pre-zygotic barriers have evolved among the sympatric species due to reinforcement.
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Parthenogenetic female populations in the brown alga Scytosiphon Lomentaria (Scytosiphonaceae, Ectocarpales): decay of a sexual trait and acquisition of asexual traits.
Journal of phycology, 2018Co-Authors: Masakazu Hoshino, Tatsufumi Okino, Kazuhiro KogameAbstract:In isogamous brown algae, the sexuality of populations needs to be tested by laboratory crossing experiments, as the sexes of gametophytes are morphologically indistinguishable. In some cases, gamete fusion is not observed and the precise reproductive mode of the populations is unknown. In the isogamous brown alga Scytosiphon Lomentaria in Japan, both asexual (gamete fusion is unobservable) and sexual populations (gamete fusion is observable) have been reported. In order to elucidate the reproductive mode of asexual populations in this species, we used PCR-based sex markers to investigate the sex ratio of three asexual and two sexual field populations. The markers indicated that the asexual populations consisted only of female individuals, whereas sexual populations are composed of both males and females. In culture, female gametes of most strains from asexual populations were able to fuse with male gametes; however, they had little to no detectable sexual pheromones, significantly larger cell sizes, and more rapid parthenogenetic development compared to female/male gametes from sexual populations. Investigations of sporophytic stages in the field indicated that alternation of gametophytic and parthenosporophytic stages occur in an asexual population. These results indicate that the S. Lomentaria asexual populations are female populations that lack sexual reproduction and reproduce parthenogenetically. It is likely that females in the asexual populations have reduced a sexual trait (pheromone production) and have acquired asexual traits (larger gamete sizes and rapid parthenogenetic development).
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Concordance between DNA-based species boundaries and reproductive isolating barriers in the Scytosiphon Lomentaria species complex (Ectocarpales, Phaeophyceae)
Phycologia, 2018Co-Authors: Masakazu Hoshino, Shozo Ishikawa, Kazuhiro KogameAbstract:Abstract: DNA-based species delimitation methods often predict many putative cryptic species. Interpretation of these putative species (i.e. do they represent distinct species, or is this an erroneous estimate based on DNA variability?) is challenging because estimates of DNA-based delimitation are often difficult to verify using nongenetic data such as morphology or geographical distribution. In the present study, estimates of DNA-based delimitation methods were verified based on the biological species concept in Japanese populations of Scytosiphon Lomentaria. Three DNA-based species delimitation methods (Generalised Mixed Yule Coalescent, Poisson Tree Processes and Automatic Barcode Gap Discovery) were conducted using mitochondrial (cox1) and nuclear (second intron of centrin gene) DNA sequence datasets. In the S. Lomentaria species complex, five putative cryptic species (Ia–Va) were well-supported by DNA-based species delimitation, and these putative species were often found in the same locality. To ve...
Chikako Nagasato - One of the best experts on this subject based on the ideXlab platform.
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NEW PYRENOID FORMATION IN THE BROWN ALGA, SCYTOSIPHON Lomentaria (SCYTOSIPHONALES, PHAEOPHYCEAE)1
Journal of Phycology, 2002Co-Authors: Chikako Nagasato, Taizo MotomuraAbstract:The Scytosiphon Lomentaria (Lyngbye) Link cell characteristically has only one chloroplast with a prominent protruding pyrenoid. We observed the appearance of a new pyrenoid in each chloroplast during first mitosis in zygotes of S. Lomentaria, using the freeze substitution technique. At first, a pyrenoid matrix appeared within the outermost stroma, in which thylakoid triplets and ribosomes were absent. At this time, the surface of this part remained smooth. The old pyrenoid was covered with a pyrenoid cap on the cytoplasmic side, whereas there was no pyrenoid cap on the new pyrenoid before protrusion. Irregularly shaped membranous sacs containing fine granular materials associated with the cytoplasmic side of the new pyrenoid. The sacs fused with each other and changed conformation and finally transformed into the pyrenoid cap. The new pyrenoid gradually protruded toward the cytoplasm, and the new pyrenoid cap became curved along the surface of pyrenoid. Cytokinesis occurred, and each chloroplast had two prominent protruding pyrenoids in two-celled zygotes. We examined immunolocalization of β-1,3-glucans within the pyrenoid cap with a monoclonal antibody, using EM. Gold particles indicating localization of β-1,3-glucans were detected in vacuoles but never in the pyrenoid cap. This observation suggests that the pyrenoid cap in brown algae contains no photosynthetic products such as polysaccharide.
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Spindle formation in karyogamy-blocked zygotes of the isogamous brown alga Scytosiphon Lomentaria (Scytosiphonales, Phaeophyceae)
European Journal of Phycology, 2000Co-Authors: Chikako Nagasato, Taizo Motomura, Terunobu IchimuraAbstract:The first spindle formation in karyogamy-blocked zygotes in the isogamous brown alga Scytosiphon Lomentaria was studied by electron and immunofluorescence microscopy using anti-centrin and anti-β-tubulin antibodies. Zygotes blocked in karyogamy by incubation at high temperature (22 °C) were compared with normal zygotes incubated at 14 °C. In normal zygotes, after the disappearance of female gamete centrioles, centrioles from the male gamete duplicated and migrated to both poles in the metaphase, and a bipolar spindle was formed. The nuclear envelope was almost intact except at the poles. In karyogamy-blocked zygotes of S. Lomentaria, both DNA synthesis and chromosomal condensation occurred in the male and female nuclei. A bipolar mitotic spindle with a pair of centrioles at each of two poles could be observed in the male nucleus, but not in the female nucleus. In some cases, after a pair of centrioles derived from the male gamete duplicated and separated, one of the two pairs migrated towards the female n...
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KARYOGAMY BLOCK BY HEAT STRESS IN THE FERTILIZATION OF BROWN ALGAE
Journal of Phycology, 1999Co-Authors: Chikako Nagasato, Taizo Motomura, Terunobu IchimuraAbstract:Karyogamy was inhibited by heat stress in zygotes of Scytosiphon Lomentaria (Lyngbye) Link (isogamy), Cutleria cylindrica Okamura (anisogamy), and Fucus distichus subsp. evanescens (C. Agardh) Powell (oogamy). Although high temperatures did not inhibit migration of the male and female nuclei, nuclear envelope fusion was blocked. The ultrastructural stage at which karyogamy was inhibited varied among these species. In S. Lomentaria, the outer membranes fused with each other, but the inner membranes did not fuse. Partial fusion of the nuclear envelope occurred in C. cylindrica. In F. distichus, the block of karyogamy at high temperature was incomplete, and nuclear fusion proceeded gradually. The block to karyogamy in S. Lomentaria zygotes was reversible, and karyogamy proceeded when zygotes were transferred from 22° to 14° C. Experiments using inhibitors suggested that proteins that might be formed de novo after fertilization do not participate in karyogamy or its inhibition at either 14° or 22° C.
